The present invention relates to a driving means for a tape-like material such as a roll film. More particularly the invention relates to a control arrangement for driving roll film which is used in microreaders or similar equipment and is of the type having at least one end fixed to a reel shaft.
An important aspect of control of unwinding and forwarding of roll film, is the detection of the end of the film, since if the end of the film is not detected there is a risk of unwinding the film too much to permit subsequent rewinding of the film. Detection of the film end is particularly important when the film end is fixed to the shaft of a film reel, and when a motor, whether controlled manually of automatically, is employed, since in such cases failure to detect the film end may result in breakage of the film, damage to the drive system, or other trouble such as overheating of the drive motor.
There have accordingly been proposed many means for detection of the end of film being unwound. In a typical conventional means, for example, there is provided a special mark near the end of a film and a detector stops the film unwinding drive system upon detection of this mark. Alternatively, as disclosed, for example, in Japanese Patent publication No. 46-43186, marks are provided in the roll film for detection of respective frames, and on the basis of the time elapsing between such marks and the time period set by a timer means, the trailing end of the roll film is detected when the particular mark is not detected for a time period more than a predetermined period of time. More specifically, if after detection of one mark, another mark is not detected within the set time, it is presumed that the film end has been reached and unwinding of film is stopped. According to another known means disclosed, for example, in Japanese Laid Open Patent Application No. 49-62126, there are provided, in a roll film, frame count slits and a transparent strip for detection of a frame position, which are detected by separate photodetection means which detect the trailing end of the film if signals representing both the detection strip and a frame count slit are not simultaneously received.
All of these conventional means have the disadvantages that they require an extra step in the manufacture of the film, to make requisite marks or slits, and also that each type of means is not employable with film which has not been specially manufactured.
Moreover, in the conventional trailing edge detecting mechanisms utilizing marks and the like, in addition to the inconveniences as described above, it is necessary to shift or reform such marks for addition or editing of the film, requiring extremely troublesome procedures in actual use, while the known arrangements utilizing timer mean have serious disadvantages such as that the time for which the timer means is set must inevitably be altered every time the feeding speed of the roll film is changed.
It is accordingly the principal object of the invention to provide a roll film drive control arrangement which, in driving of a roll film having at least one end fixed to a film reel shaft, automatically detects the film end and stops film unwinding, but does not require any special preparation of the film and so is employable in association with all types of roll film.
It is another object of the invention to provide a roll film drive control arrangement of the above described type which functions accurately and includes a control circuit portion which may easily be provided as a separate unit.
It is a further object of the present invention to provide a roll film drive control arrangement of the above described type which is simple in construction and can be readily incorporated into a conventional roll film drive arrangement at low cost.